A loud bang on Kokotau Rd outside Parkvale Mushrooms on Sunday morning signalled the start of an hour-long and careful extrication of a trapped motorist following a two-car collision.

Parkvale workers rushed outside to find a 4x4, towing a trailer loaded with a quadbike and deer carcasses, and a Toyota Spacio had collided head-on shortly after 11am.

The female driver of the Spacio was trapped with torso and leg injuries, but was conscious and talking while Carterton and Greytown fire crews cut away both doors on her side so that Wellington Free Ambulance paramedics could reach her.

A dog, which was travelling with her, was unharmed.

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An early decision was made to call Life Flight for the Westpac Rescue helicopter, which landed in a field beside the road.

After receiving medication the woman was eased onto a stretcher and taken to the helicopter. Her condition at Wellington Hospital is stable.

The two men who had been in the 4x4 vehicle had scratches but were otherwise uninjured.

They made no comment to media. A Parkvale employee, who did not want to be named, said "hell, yes" when asked if there had been crashes like this outside their work before.

"I've been working here 30 years, and I've seen a few."

She said the sound was like "a big explosion".

"I know that sound, I knew it was bad."

Police said the occupants of the 4x4 were assisting them with their inquiries.

A Serious Crash Investigation would be undertaken, they said.